Abstract：Research purposes: In combination with the tunnel engineering of Line 2 of Xi＇an，and according to the specific geological conditions，the FLAC3D numerical simulation software was used to determine the safety range of the supporting force on the excavation face during the tunnelling，taking the settlements of the ground above the excavation face and the tunnel top as the measuring standard，for the purpose of avoiding the over settlement and rising of the ground when the tunnel passed through the place with big variation of the buried depth．
Research conclusions: ( 1 ) The excavation face of shield tunnel has its minimum supporting force and maximum supporting force． It means that the supporting force has a reasonable safely range． When the supporting force is out of range，the soil around the tunnel is easy to be damaged，or the over settlement or over rising appears to the ground surface when the tunnel is shallow． ( 2) When the tunnel buried depth is bigger than 1． 5 times of the tunnel diameter，the surface point can not effectively reflect the deformation of soil around the tunnel，and at this time，the soil deformation should be monitored and controlled by the monitoring spots in the tunnel． ( 3) The safely range of supporting force increases with the increase of the tunnel depth． When the tunnel is shallow， the safely range of supporting force is very small，and at this time，the heap loading on the ground should be used to increase the tunnel buried depth equivalently for increasing the supporting safely range and reducing the construction difficulty．
颜治国，李岳. 西安地铁隧道盾构开挖面支护力安全范围分析[J]. 铁道工程学报, 2012, 29(7): 82-86.
YAN Zhi － guo，LI Yue. Analysis of Safety Range of Supporting Force on Excavation Face of Tunneling Shield for Xi＇an Metro. 铁道工程学报, 2012, 29(7): 82-86.
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2012, Vol. 29 
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